There are known compositions which form polymer micelles as a drug carrier, by encapsulating a poorly-water-soluble drug in a block copolymer which includes a hydrophilic segment and a hydrophobic segment bonded together, and methods for producing the composition. Particularly, block copolymers which comprised of a polyethylene glycol derivative as a hydrophilic segment and a polyamino acid or a derivative thereof as a hydrophobic segment, have a nature to form self-associating micelles easily in water with relative ease. Therefore, such block copolymers are used as carriers for drug delivery systems (Patent Literature 1).
To make a such composition, there have been also known in the art a method comprising once dissolving such a block copolymer and a poorly water-soluble drug in an organic solvent, then distilling off the solvent, and dispersing the residue in water (see Patent Literature 2 and Patent Literature 3).
A method for powderizing a water-soluble drug by spray drying is disclosed in Patent Literature 4. Also, a method for powderizing a melted polymer by spray cooling is disclosed in Patent Literature 5.